1. Field of the Invention
The present invention relates to a solid electrolytic capacitor including an anode made of a valve action metal such as aluminum, tantalum or niobium, and also including a solid electrolyte such as a conductive polymer or manganese dioxide. The present invention also relates to a method for manufacturing the solid electrolytic capacitor.
2. Description of the Prior Art
A typical solid electrolytic capacitor including a valve action metal for an anode is manufactured in the following manner. First, an anode is made of a porous compact of the valve action metal such as a surface-roughened aluminum foil or a porous compact of a sintered powder of a valve action metal such as tantalum or niobium. The entire surface of the porous compact of the valve action metal is covered with a dielectric oxide film. Secondly, a solid electrolytic layer of a conductive polymer such as polypyrrole or manganese dioxide is formed on the surface of the dielectric oxide film, and a cathodic layer of a carbon layer, a silver layer or the like is formed on the solid electrolytic layer. Subsequently, an anodic extraction terminal is attached to an anodic lead by welding or the like, and a cathodic extraction terminal is attached to a cathodic layer with a conductive adhesive or the like. Lastly, the entire element is covered with a packaging resin from which the cathodic extraction terminal and the anodic extraction terminal are partially exposed to the outside. Alternatively, the solid electrolytic layer can be connected electrically with the cathodic extraction terminal without forming a cathodic layer.
Since the packaging resin serves to maintain airtightness from the outside, it should be adhered securely to electrode extraction members such as a lead, a foil and a terminal. Especially, when the solid electrolyte is a conductive polymer, insufficient airtightness will cause considerable deterioration and thus, the electric properties will be difficult to maintain favorably for a long time. Therefore, for securing the airtightness, the packaging resin is formed generally from an epoxy-based thermosetting resin, using molding (a tip capacitor) or dipping (a lead capacitor).
A solid electrolytic capacitor having a case instead of a packaging resin is also known. Such a capacitor is manufactured by inserting an entire element in a case where a cathodic extraction terminal and an anodic extraction terminal are partially extracted outward, and by sealing the opening of the case with a resin or the like. The case is an insulator such as a resin or ceramic, or a metal having an insulated portion for a connection with terminal parts.
Generally, an electrolytic capacitor including an electrolytic solution can repair defects on a dielectric oxide film caused during a manufacturing process. Therefore, leakage current will not be increased considerably. However, a solid electrolytic capacitor including a solid electrolyte does not have sufficient capability to repair the dielectric oxide film. Such a dielectric oxide film cannot self-repair defects thereon. When the dielectric oxide film deteriorates due to stresses in manufacturing, such as mechanical stress and thermal stress, the leakage current tends to increase.
Conventionally, solid electrolytic capacitors are aged to decrease leakage current by applying a predetermined dc voltage to an interface between the anodic and cathodic terminals before or after formation of the package. In an aging, a film is repaired using water that has been absorbed from the atmosphere as an electrolytic solution. However, since this repair depends on moisture absorption, a conventional aging requires a long period to provide a stable leakage current property.
JP-A-5-243096 discloses a method to insulate a conductive polymer used for a solid electrolyte with Joule heat by concentrating a current on a part with lowered voltage resistance. However, when the defect is large, the insulation may be insufficient and the leakage current cannot be decreased.
A purpose of the present invention is to provide a solid electrolytic capacitor capable of decreasing a leakage current with a further efficiency when compared with a capacitor aged under an influence of moisture absorption, and also to provide a method for manufacturing the capacitor.
A solid electrolytic capacitor of the present invention includes a capacitor element inside a packaging material. The capacitor element includes a valve action metal, an oxide film layer formed on a surface of the valve action metal, a solid electrolytic layer formed on the oxide film layer, and contains an organic compound having a boiling point of not lower than 150xc2x0 C. and a melting point of not higher than 150xc2x0 C.
A method for manufacturing a solid electrolytic capacitor of the present invention includes a step of providing a capacitor element with an organic compound having a boiling point of not lower than 150xc2x0 C. and a melting point of not higher than 150xc2x0 C., and arranging the capacitor element containing the organic compound inside a package.
Accordingly, because of the organic compound, a solid electrolytic capacitor can be aged more efficiently when compared to a conventional method, and a solid electrolytic capacitor with less leakage current can be provided easily.